Dust beats biology for cloud ice formation

Liz Kalaugher in Environmental Research Web: Biological particles have been touted as potential key players in the nucleation of ice particles in clouds, as they are able to help ice form at warmer temperatures than many other aerosols. But new modelling work in Norway and Germany indicates that biological particles are not that important for cloud ice formation after all.

"We are confident now that on a global scale, biological particle concentrations are too low to play a significant role in cloud ice formation, and that instead mineral dust is the major component," Corinna Hoose from the University of Oslo, Norway and Karlsruhe Institute of Technology, Germany told environmentalresearchweb. "This is in agreement with many measurements of ice crystal residuals."

Together with colleagues from Oslo and the Max Planck Institute for Chemistry, Germany, Hoose calculated that biological particles contributed a maximum of 0.6% to the global average ice nucleation rate. The team used the CAM–Oslo aerosol climate model and newly available estimates and laboratory measurements to come up with their results.

…Ice nucleation in clouds is of particular interest as it is the first step in the creation of snow and most types of rain. Previously, high concentrations of biological ice nuclei have been found in a wave cloud over Wyoming and in the Amazon basin, and the particles have been found to be ubiquitous in precipitation on different continents. "[Our study] means that living or dead micro-organisms are less involved in cloud ice and precipitation formation than has been speculated, and that the observed cases with high biological ice nucleus concentrations are not representative of average atmospheric conditions," said Hoose....

Cumulus clouds just floating along, shot by Michael Jastremski., Wikimedia Commons, under the Creative Commons Attribution-Share Alike 2.0 Generic license.